From the Overview: "What are they? Antidumping (AD) and Countervailing Duties (CVD) address unfair trade practices by providing relief to U.S. industries and workers that are 'materially injured,' or threatened with injury, due to imports of like products sold in the U.S. market at less than fair value (AD), or subsidized by a foreign government or public entity (CVD). What is the relief provided? At the end of an investigative process, in AD cases, the remedy is an additional duty placed on the imported merchandise to offset the difference between the price (or cost) in the foreign market and the price in the U.S. market. In CVD cases, a duty equivalent to the amount of subsidy is placed on the imports."
CRS In Focus, IF10018
Congressional Research Service: https://crsreports.congress.gov/